Method For Conducting Electrosurgery With Increased Crest Factor

ABSTRACT

A method for conducting electrosurgery using increased crest factors employs an electrosurgical instrument having at least one conductive element that is surrounded by an insulation layer except at a conductor edge portion of the conductive element. The conductor edge portion and insulation layer each having unique geometric shapes and composition of the parts concentrate the electrosurgical power, reduce or eliminate the production of smoke and eschar and reduce tissue damage. The outer profile of the insulation layer and conductive element are configured to facilitate the flow of electrosurgical decomposition products away from the conductor edge where they are formed. The combined effects of the electrosurgical instrument configurations enable safe use of crest factors of 5 or greater in electrosurgical procedures.

This application claims the benefit of priority to U.S. ProvisionalApplication 60/695,692 entitled Multielectrode ElectrosurgicalInstrument filed Jun. 30, 2005, the entire contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to surgical methods and apparatus, andmore particularly to applying electrosurgical power to a tissue site toachieve a predetermined surgical effect.

BACKGROUND OF THE INVENTION

The potential applications and recognized advantages of employingelectrical energy in surgical procedures continue to increase. Inparticular, for example, electrosurgical techniques are now being widelyemployed to provide significant localized surgical advantages in open,laparoscopic, and arthroscopic applications, relative to surgicalapproaches that use mechanical cutting such as scalpels.

Electrosurgical techniques typically entail the use of a hand-heldinstrument that contains one or more electrically conductive elementsthat transfer alternating current electrical power operating at radiofrequency (RF) to tissue at the surgical site, a source of RF electricalpower, and an electrical return path device, commonly in the form of areturn electrode pad attached to the patient away from the surgical site(i.e., a monopolar system configuration) or a return electrodepositionable in bodily contact at or immediately adjacent to thesurgical site (i.e., a bipolar system configuration). The time-varyingvoltage produced by the RF electrical power source yields apredetermined electrosurgical effect, such as tissue cutting orcoagulation.

During electrosurgical procedures electric current flows through one ormore conductive elements, the active electrodes, and transferselectrical current to tissues, often with coincident sparks or arcs ofelectricity occurring between one or more electrodes and tissues. Theoverall process causes heating of tissue and the electrode metal. Tissueheating causes tissues to break into fragments or otherwise change intomaterials that generally differ physically and chemically from thetissue before it was affected by electrosurgery. The tissue changes atthe surgical site, such as charring, interfere with normal metabolicprocesses and, for example, kill tissues that remain at the surface ofincisions. The changes in tissues caused by electrosurgical energy, suchas killing parts of tissues, are known to interfere with healing at thesurgical site.

Beyond damaging tissue at the surgical site, conventional electrosurgeryhas other drawbacks which limit its applicability or increase the costsand duration of procedures. Induced heating of tissues and electrodescauses smoke plumes to issue from the tissue. Smoke obscures the fieldof view and hinders surgical procedures and is also a known healthhazard. Controlling smoke once it has formed is problematic, requiringthe evacuation of large volumes of air in order to capture anappreciable fraction of the smoke with wands that are close to thesurgical site where they are in the way, and adds costs in bothadditional equipment and labor.

The induced heating also generally causes tissue that has been alteredby electrosurgery to adhere to and partially coat electrosurgicalelectrodes. The tissue fragments that adhere to electrodes and coat theelectrodes is called “eschar.” The coatings on blades that form fromtissue and tissue fragments are typically rich in carbon and containvarious compounds that tend to make the coatings electrically conductivewhen energized by the type of power used for electrosurgical procedures.Eschar inhibits the effectiveness of electrosurgical devices and mustfrequently be removed, hindering surgical procedures.

Despite advances in the field, electrosurgical blades continue to sufferfrom one or more of the problems of producing smoke, having materialsfrom tissues coat the blades, and damaging tissue. Therefore, a needexists to improve performance in each of these areas. Historically,electrosurgical blades have generally not given consideration to thechemical reaction environment and conditions that occur where theelectrosurgical energy interacts with tissue by considering factors suchas the propensity of tissue to become trapped in regions that lead toprolonged residence times at reactive conditions that lead to producingsmoke and materials that coat blades to form eschar. Likewise, prior artelectrosurgical blades did not consider the conductive pathways that canbe formed by tissue fragments adhering to blades and the effects thatthese built-up conductive pathways have on producing smoke, producingmore materials that can further coat blades, and the effects that thesehave during electrosurgery.

The aforementioned limitations in conventional electrosurgery imposelimits on the peak voltage that can be applied to tissue duringelectrosurgery.

SUMMARY

Various embodiments provide a method for conducting electrosurgery withhigher crest factors, which is the ratio of the peak voltage to the rootmean square (RMS) voltage applied to tissue. By increasing the safe andeffective crest factor, enhanced therapeutic effects are enabled.

The various embodiments use electrosurgical instruments having a bladegeometry, blade composition or a combination of blade geometry andcomposition that concentrates electrosurgical energy and reduces orprevents smoke production, eschar accumulations, and/or tissue damage.The embodiment instruments focus electrosurgical energy to a smallamount of tissue for a short duration compared to the amount of tissueand duration than is customary during electrosurgery using conventionaltechnology. Various embodiments yield less eschar accumulation on theelectrosurgical instrument by providing an exterior surface of theinstrument with a shape that facilitates movement of tissuedecomposition products away from the active region of the conductiveelement. The active region is a region on the conductive element whereelectrosurgical energy transfers from the blade to tissue. In someembodiments, the tapered configuration includes an electricallyconductive element with a tapered section. In some embodiments, thetapered configuration includes configuring an insulating layer with atapered section. In various embodiments, insulation on the conductiveelement has a surface free energy that reduces the propensity forelectrosurgical decomposition products (defined herein) to stick to thesurface. In various embodiments, the shape of the blade minimizes theduration that the active region is near any particular portion of tissueas the blade is moved through tissue as during an incision.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate embodiments of the invention,and, together with the general description given above and the detaileddescription given below, serve to explain features of the invention.

FIG. 1 portrays a cross-section of a blade that has been insulatedwhereby the outer taper to the edge is defined by a single smooth curveat the conductor edge.

FIG. 2 portrays a magnified section of the region where electrosurgicalenergy interacts with tissue for the blade illustrated in FIG. 1.

FIG. 3 portrays a magnified section of the region where electrosurgicalenergy interacts with tissue for the blade illustrated in FIG. 2 andshows the blade depth and half-width.

FIG. 4 portrays a cross-section of a blade with a conductive elementthat has a concave taper that has been insulated whereby the outer taperto the edge is not defined by a single smooth curve at the conductoredge.

FIG. 5 portrays a cross-section of a blade with a conductive elementthat has a substantially flat taper that has been insulated whereby theouter taper to the edge is not defined by a single smooth curve at theconductor edge.

FIG. 6 portrays a cross-section of a blade with a conductive elementthat has a concave taper that has been insulated whereby the outer taperto the edge is not defined by a single smooth curve at the conductoredge and that shows the insulation angle.

FIG. 7 portrays a cross-section of a blade with a conductive elementwhere the outer taper to the edge is defined by a single smooth curve atthe conductor edge showing the insulation angle.

FIG. 8 portrays a cross-section of a blade with a conductive elementthat has a concave taper that has an overall profile that has a taperthat transitions from curved to approximately flat at the edge of theblade.

FIG. 9 portrays a cross section of a blade having a conductive elementthat has a concave taper and a concave overall taper to an edge.

FIG. 10 portrays a side view of a blade with two exposed edges at anobtuse angle.

FIG. 11 portrays a side view of blade with two exposed edges at anobtuse angle in relation to making a tissue incision.

FIG. 12 portrays a side view of blade with two exposed edges at an acuteangle in relation to making a tissue incision.

FIG. 13 portrays a side view of blade with one exposed edge in relationto making a tissue incision.

FIG. 14 portrays a side view of a needle electrode in relation totissue.

FIG. 15 illustrates an electrosurgical instrument including a holder andblade according to an embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The various embodiments will be described in detail with reference tothe accompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

As used herein, the terms “about” or “approximately” for any numericalvalues or ranges indicates a suitable dimensional tolerance that allowsthe part or collection of components to function for its intendedpurpose as described herein. Also, as used herein, the terms “patient”,“tissue” and “subject” refer to any human or animal subject and are notintended to limit the systems or methods to human use, although use ofthe subject invention on a human patient represents a specificembodiment.

All devices that may be used to produce a predetermined surgical effectby applying RF power to tissue may be referred to herein aselectrosurgical “blades” due to their function of partial or completeremoval of one or more parts of tissue (including changing the structuresuch as by at least partially denaturing or decomposing), regardless oftheir size, shape, or other properties. Use of the term “blade” hereinis not intended to restrict the description or any embodiment to aparticular shape or configuration. While various embodiments pertain togenerally planar elements which may resemble a conventional scalpelblade, other embodiments encompass element configurations which aredissimilar from conventional blades, including, for example, needle,hook and curved configurations.

Reference herein to the purpose and effects of electrosurgical devicesas producing “a predetermined surgical effect” encompasses all potentialeffects generated during electrosurgery. The predetermined surgicaleffect include, but are not limited to: causing a partial or completeseparation of one or more tissue structures or types, including, but notlimited to making electrosurgical incisions; cause partial or completeremoval of one or more parts of a tissue; changing the structure oftissue, such by at least partially denaturing or decomposing tissue;cutting; hemostasis (such as by inducing coagulation); tissue welding;tissue sealing, and tissue shrinking. Commonly, multiple predeterminedsurgical effects occur simultaneously, such as cutting and hemostasisboth occurring as incisions are made.

Although they may have various forms, all sources of RF power used topower electrosurgical blades will be referred to herein aselectrosurgical units and abbreviated by ESU.

The terms “electrode” and “conductive elements” are used interchangeablyherein to refer to similar structures without intending to communicateor imply a difference in structure or limitation on any embodiment orclaim of the present invention.

Electrosurgical devices come in two common varieties, monopolar andbipolar. Monopolar electrosurgical blades connect to an ESU using a wirewhile a separate return pad is connected to the ESU by another wire.Bipolar electrosurgical blades connect a set of one or more activeelectrodes to the ESU with one or more wires and connect another set ofone or more return electrodes to the ESU with one or more other wires,wherein the active electrode or electrodes and return electrodes orelectrode are connected together so that RF energy may be conveyedthrough one or more conductive media that contact at least one tissuewith such connections between electrodes being either permanent ortemporary, such as by being separately inserted into a clamping deviceor a handle with such connection being fixed or moveable, such as asliding connection.

The present inventors have recognized that reducing the amount of energyapplied to tissue reduces tissue breakdown and that the amount ofapplied energy can be reduced by reducing the exposure toelectrosurgical power (where electrosurgical power is the rate at whichelectrosurgical energy is applied) either by reducing the power level,the time of exposure to electrosurgical power, or by reducing both thepower level and the time of exposure. Various embodiments reduce theamount of energy to which tissue is exposed by proper selection of bladegeometry, blade materials, and the amount of power used.

More generally in this regard, energy discharge from electrosurgicalinstruments may be in the form of electrical energy and/or thermalenergy. Electrical energy is transferred whenever the electricalresistance of a region between an electrosurgical instrument and tissuecan be broken down by the voltage of the electrosurgical power. Thermalenergy is transferred when thermal energy that has accumulated in theelectrosurgical instrument overcomes the thermal resistance between theinstrument and the tissue (i.e. due to temperature differencestherebetween) and is transferred to tissue by conduction, radiationand/or convection. Transferring electrosurgical energy to tissue occursat portions of the electrosurgical instrument which cause the desiredsurgical effect, such as forming an incision. Such portions of theinstrument are called functional areas. All other portions of theelectrosurgical instrument are nonfunctional, and transfer ofelectrosurgical energy to tissue from these portions should beminimized. Electrosurgical energy may be transferred to tissue withoutdirect contact with the functional area by means of electrical sparksand radiative and convective heat transfer. As used herein, the term“contact” relating to the position of blades or electrodes near tissueencompasses both actual contact and positioning of a functional areaclose enough to tissue for transfer of electrosurgical energy to occur.

Pyrolysis is the breakdown of molecules into smaller moieties by theaction of heat (physical fragmentation), typically followed bysubsequent recombination of these thermal fragments to form largerspecies. As used herein, the term “electropyrolysis” refers to theprocess whereby electrical energy in the form of sparks or arcsinteracts with tissue to break down tissue constituents by heat,electron interactions with materials, photon interactions withmaterials, or any combination of these.

In general terms, electrosurgery is the process by which high voltage(e.g., voltages greater than about 100 volts) electrical power isapplied to tissue to achieve a predetermined surgical effect. Suchvoltages are typically employed as high frequency (e.g., frequenciesgreater than about 5 kHz) and most commonly use frequencies greater thanabout 100 kHz to reduce neuromuscular stimulation. The energy istransferred to tissue at the surgical site using one or more electrodes.Electrical energy is transferred as well as thermal energy which comesfrom electrodes becoming hot as electrical power moves through them,producing I²R power losses which manifest themselves as heat, some ofwhich is transferred to tissue via conduction, radiation, andconvection. As used herein, the term “electrosurgical energy” refers toall of the energy transferred to tissue during electrosurgery,regardless of form or transfer mechanism, and including both electricaland thermal energy.

Without restriction to any particular theory of operation regarding itsform or method of use, the following descriptions of processes duringelectrosurgery are provided to illustrate one or more candidateprocesses that could be present during electrosurgery to facilitatesubsequent descriptions of the various embodiments.

Tissue breaks down where sparks or hot metal contact it. This breakdownof tissue is believed to be caused by rapid heating of tissue whereelectrosurgical energy, principally electrical sparks and thermal energyfrom hot metal, contacts tissue and electropyrolysis and hydrolysis lysetissue constituents.

During electrosurgery a variety of reaction products are produced.Electropyrolysis is believed to be a cause of tissue breakdown duringelectrosurgery. One result of electropyrolysis during electrosurgery isthe production of hot water and steam which promote hydrolysis oftissues. For example, electropyrolysis and hydrolysis are believed tobreak down proteins and produce a range of products, including cyclicand linear polypeptide materials. Electropyrolysis is also believed tobe the process by which electrosurgery is able to cut or otherwise breakdown tissues that have a cellular structure (e.g., muscle tissue) aswell as tissues that do not have a cellular structure (e.g., collagenfibrils in ligaments).

Beyond electropyrolysis products, other electrosurgery products are alsoformed. Most notable are changes in state in which materials changetheir state (e.g., steam forming when water changes from liquid to gas)but are otherwise not changed chemically. During electrosurgery someproducts have altered structure, but otherwise retain their chemicalidentity, such as when proteins denature and then refold into shapesdifferent from those prior to denaturation. During electrosurgery someproducts retain their chemical structure and state, but changephysically in other ways (e.g., air being heated so that its specificvolume increases).

Finally, some electrosurgery processes can cause materials, such ascellular contents or viral particles, to be liberated or moved with astream of other materials, such as being conveyed by flowing steam orhot air produced during electrosurgery.

Collectively, all of the materials produced or altered duringelectrosurgery, including those from electropyrolysis, change of state,change of structure, change of volume, and liberation are referred toherein as the “products of electrosurgery,” “electrosurgicaldecomposition products,” or “electrosurgical products”. The collectionof processes that break down or alter tissues during electrosurgery arereferred to here as electrosurgical tissue decomposition processes.

Some of the resulting materials form smoke or steam and some of theresulting materials form substances that stick to blades. Whenelectrosurgery is performed in a gaseous environment, such as air orcarbon dioxide, particularly when incisions are made, a common resultusing conventional technology is a smoke plume. The smoke plume isbelieved to consist primarily of pyrolysis and electropyrolysisproducts, including steam and hot air along with materials such ascellular contents and other entrained materials.

When electrosurgery is performed, including when incisions are made,some of the products of electrosurgery form deposits on electrodescontacting or in close proximity to tissue. These deposits, calledeschar, are believed to begin forming when sticky materials, such asdenatured proteins, adhere to electrode surfaces. Other materials mayalso be mixed in with the sticky materials. As electrosurgery proceeds,thermal energy continues to pyrolyze these materials on the electrodesleading to the production of substances having a higher carbon:hydrogencontent than the starting materials. Some resulting materials conductelectricity at the voltages used, perhaps due to the presence of ionsfrom salts or by having high carbon contents, and form an electricallyconductive coating on the blade, even if the blade's surface is coatedwith an insulating coating. Therefore, eschar formation on the outsideof an insulated electrode that has, for example, only an edge exposed,can have an electrically active area that extends from the exposed edgebecause of conductive eschar deposits forming on the blade's surface andbeing in electrical contact with the exposed edge. This conductivedeposit can expose more tissue to prolonged exposure to electricalenergy.

The amount of electrosurgical products produced depends upon the amountof energy applied to tissue, the rate at which the energy is applied,and the length of time that tissue is exposed to sources of the energy.While conventional electrosurgical systems have attempted to controlthese factors by means of ESU settings, the present inventors haverecognized that the configuration of electrosurgical blades also affectthe time and amount of energy applied to portions of tissue, and thus tothe generation of electrosurgical products. For example rough bladefunctional surfaces tend to retain tissue fragments and thus expose suchtissue fragments to electrosurgical energy for longer durations thanoccurs when the blade has smooth functional surfaces. If recesses orpockets exist where material can be held in place in close proximity tothe functional surfaces, the residence time for chemical reactions tooccur increases for trapped materials. With increased residence time,more lysis occurs, leading to increased smoke and eschar production. Aslow molecular weight materials are lysed from trapped materials theyleave as smoke and gases that are relatively rich in hydrogen, leavingbehind an increasingly carbon-rich material. This material is eschar.When deposited on the surface of an insulating layer it effectivelywidens the electrically conductive edge, which exposes more tissue toelectrosurgical energy and increases the time at which tissue is exposedto lysing conditions. Exposing more tissue to lysing conditions andexposing tissue for longer periods to such conditions causes more smokeand eschar to form, and thus it is desirable to prevent or reduce theoccurrence of such conditions.

Using cutting as an example electrosurgical process, the power settingstypically used during electrosurgery employing conventionalelectrosurgical systems are over 30 Watts, and often are on the order of40 to 100 Watts. Theoretically, the amount of power required for cuttingis much lower, between about 2 and 15 Watts. The surplus power beyondthat theoretically required drives unwanted reactions such as theproduction of smoke and eschar as well as overheating tissue that killscells.

The various embodiments employ blade geometry, blade composition or acombination of blade geometry and composition to reduce or prevent smokeproduction, eschar accumulations, or tissue damage. The embodimentsfocus electrosurgical energy to a small amount of tissue for a shortduration compared to the amount of tissue and duration than is customaryduring electrosurgery using conventional technology. In the embodiments,the electrosurgical energy flows from a conductive element that issurrounded by insulation except for an exposed edge or point. Providinga relatively small exposed edge or point on the conductive elementrestricts RF energy flow to this portion of the conductive element,minimizing energy transfer from the rest of the conductive element whichis covered by insulation. In some embodiments, the exposed edge on theconductive element can be formed by tapering down the insulationcovering from its thickness at the wide part of the conductive elementto minimal thickness adjacent to the exposed edge, as illustrated inFIGS. 4 and 5. In other embodiments, the conductive element geometryends in a point that is not covered by insulation, as also illustratedin FIGS. 4 and 5.

Various embodiments comprise electrosurgical instruments that use bladeshape and composition to reduce the production of smoke and eschar by,among other methods, reducing the time that materials are exposed toelectrosurgical energy. The result is reduced smoke production, reducedeschar production, and reduced tissue damage.

Various embodiments include electrosurgical instrument features thatpromotes the free flow of electrosurgical decomposition products such assteam, gases, and vapors away from regions near the functional surfaceswhere electrosurgical energy interacts with tissue and such gaseousdecomposition products form. It is believed that facilitating the flowof gaseous decomposition products away from the functional surfaceswhere they are generated reduces the local gas pressure in the vicinityof the functional surfaces which would otherwise rise with the buildupof gaseous products. By reducing the pressure and promoting the flow ofelectrosurgical decomposition products, the conditions which causepyrolysis and electropyrolysis of tissue and electrosurgical productsare reduced, particularly in the vicinity of the functional surface justremoved from where the desired electrosurgical effect occurs. It isbelieved that continued pyrolysis and electropyrolysis ofelectrosurgical decomposition products leads to more generation of smokeand eschar. Thus, by reducing pressure, and thus temperatures, in thevicinity of the functional surfaces and facilitating the escape ofelectrosurgical decomposition products, generation of smoke and escharcan be substantially reduced.

In various embodiments, the electrosurgical instrument or blade featuresa narrow surface, edge or point in the vicinity of the functional areathat reduces the length of the path that gases or vapors must traversefrom the point of generation to reach ambient conditions, thus thedistance and time during which decomposition products are exposed tohigh temperatures. In such embodiments, examples of which areillustrated in FIGS. 4-9, the functional surface is an edge of the bladethat has at least one dimension (such as thickness) which is less thanthe corresponding dimension (such as thickness) of nonfunctionalsurfaces. In various embodiments, the edge or point is comprised of ametal conductor that is surrounded by insulation except for a sectionwhere the metal is exposed. In such embodiments, the outer profile ofthe insulation where the metal conductor is exposed is thinner than theouter profile at a distance removed from the exposed surface. In anembodiment, the edge or point is shaped so that it forms an acute anglewhere it comes in close contact with tissue during use. This aspect ofthe embodiments reduces the local gas pressure compared to, for example,a blade that has a relatively flat surface shape adjacent to thefunctional surface, such as when the combination of the insulation andconductive element form a round or parabolic profile, such asillustrated in FIGS. 1 and 2. In some embodiments, the edge is formed bytapering the profile so that the radial dimension at the functionalsurface is less than the radius of part of the nonfunctional surface ofthe blade. This configuration is not limited to planar blades and in anembodiment is employed in an electrosurgical instrument having agenerally circular cross section, a configuration that is most commonlyreferred to as a needle electrode, such as illustrated in FIG. 14.

In other embodiments, the shape of the blade is configured such thatwhen it contacts tissue and is moved through tissue, the amount of timethat a tissue surface is adjacent to the functional surface is reducedor minimized. In some embodiments, the shape of the blade is configuredsuch that it substantially has only a single line or point of contact ofthe functional surface with tissue. Such embodiments differ fromconventional electrosurgical blades which typically allowelectrosurgical energy to flow into tissue from both the edge and thesides of the blade. Some embodiments, an example of which is illustratedin FIG. 13, also differ from conventional blades that have two edgesthat are substantially not collinear, such as come to a form a 120degree angle as illustrated in FIG. 10, such that one of the edges couldbe held approximately parallel to the tissue during use. Conventionalblades of this configuration allow the same section of tissue to beexposed to electrosurgical energy over the entire time that the parallelsection contacts the section of tissue, as illustrated in FIG. 11.

In various embodiments, the electrodes have functional surfaces in whichthe conductive elements are strictly convex in shape and thus do notcontain recesses. Strictly convex surfaces do not have recesses in whichtissue or electrosurgical decomposition products may become trapped. Iftissue or electrosurgical decomposition products becomes momentarilytrapped in a recess, such materials are exposed to electrosurgicalenergy and high temperature for a longer time, leading to generation ofsmoke and eschar. Such embodiments differ from conventional blades whichhave a nonconvex surface of the outer insulating surface where itextends to the edge of a metal electrode leaving the electrode slightlyrecessed into the insulation.

In various embodiments, the blade includes an outer insulating layermade of one or more materials selected to reduce thermal/electricaldischarge from non-functional portions of the electrodes. In anembodiment, such an insulating layer surrounds at least a portion ofbipolar electrodes. In various embodiments, the outer insulating layerhas a thermal conductance of about 1.2 W/cm2° K and a dielectricwithstand strength of at least about 50 volts. Such an insulating layermay advantageously comprise one or more materials with pores that havebeen sealed on the exterior surface to prevent biological materials fromentering the pores. In an embodiment, such sealing material may containone or more of various silicate materials or materials that formsilicates. In an embodiment, at least part of the outer insulating layeror the substance bonding at least one pair of electrodes may compriseone or more materials that include one or more silicate materials andone or more hydrolysable materials that in combination form a thermallyinsulative substance that by itself is essentially hydrophobic and doesnot allow biologic material to penetrate its surface.

In various embodiments, one or more of the electrodes are metal with theelectrodes having a thermal conductivity of at least about 0.35 W/cm °K. Such electrode metals may comprise a metal selected from the group:gold, silver, aluminum, copper, tantalum, tungsten, columbium, andmolybdenum, and alloys thereof. In various embodiments, one or more ofthe electrodes may be coated or plated with a substance or element thatimparts resistance to oxidation, such as a plating of gold or silver.

In some embodiments of a bipolar blade, the electrodes comprise threeconductive layers spaced apart by intermediate electrical insulationlayers, wherein the intermediate layer defines a peripheral edge portionof reduced cross-section (e.g., about 0.001 inches thick or less) forelectrosurgical power or direct current power transmission. Such anintermediate layer may comprise a metal having a melting point of atleast about 2600° F.

A heat sink structure may be included in various embodiments toestablish a thermal gradient in the blade away from functional areas(i.e., by removing heat from the electrode). In an embodiment, the heatsink structure comprises a phase change material that changes from afirst phase to a second phase upon absorption of thermal energy from theelectrodes.

In various embodiments, the insulation is selected and fabricated so ithas a surface free energy that reduces the propensity forelectrosurgical decomposition products to stick to the surface. In someembodiments, at least the edge of the conductive element is composed ofa material that reduces the propensity for electrosurgical decompositionproducts to stick to the surface and that is configured with a geometrythat promotes the flow of thermal energy away from the edge whenelectrosurgical energy is being applied to tissue.

In the various embodiments, at least one electrically conductive elementis electrically connected to an ESU. When connected to an ESU, RFcurrent will flow from the electrically conductive element whencontacting or in close proximity with an electrically conductive mediumsuch as tissue or an electrically conductive liquid or vapor.

The various embodiments described generally above maybe understood byreference to the example embodiments illustrated in the figures, whichwill now be described in more detail.

Referring to FIG. 1, an electrically conductive element 1, which istypically metallic, can be surrounded by insulation 2. The conductiveelement 1 may be of any number of shapes, such as, but not limited to:substantially flat; having one or more curves; shaped as closed curves,such as rings or hoops; shaped as nonclosed curves, such as semicirclesor crescents; planar; nonplanar, such as curved spatulas; having bendsor curves, such as hooks; encompassing volumes, such as cups orcylindrical volumes; substantially blunt; having one or more regionsthat taper from one thickness to a lesser thickness; having opposingfaces, such as forceps or scissors; and having one or more openings,such as holes, meshes, pores, or coils.

The conductive element 1 can have a tapered section 3. Additionally, theinsulation 2 can have a tapered section 4. The combination of tapers onthe conductive element 1 and the insulation 2 can produce bevels thattransition down to the conductor edge 5. This leaves the conductor edge5 exposed (i.e., not covered by insulation) so that electrical energycan transfer to tissue from the edge via conduction or capacitiveelectrical coupling, or both conduction and capacitive coupling,including with or without other energy transfer mechanisms that may befacilitated by an exposed edge including energy conveyed by conductionor radiation or a combination of conduction and radiation. Theconductive element tapered section 3 provides a cross sectional profilethat reduces the width of the conductive element 1 to form the conductoredge 5. The tapered section 3 may be reduced on one side of the profileor both, and may take on a variety of shapes as the width is reduced.For example, the cross sectional profile may include a radius ofcurvature that produces a concave profile, as illustrated in FIG. 1. Asanother example, the cross sectional profile may have a predominatelyflat profile, as illustrated in FIG. 5. Further, the cross sectionalprofile may have multiple radii of curvatures producing a crosssectional profile which combines concave and convex sections.

The conductor edge 5 is the portion of the conductive element 1 exposedfrom the insulation 2. In some embodiments, the conductor edge 5 ispositioned at the edge of the blade. The conductor edge 5 is intended tobe used in close proximity or touching tissue 6, as illustrated inFIG. 1. A narrow gap region 7 between the conductor edge 5 and tissue 6is where electrosurgical energy interacts with tissue 6 via thetransmission of electrosurgical energy.

In the blade configuration shown in FIG. 1, the outer profile of the tipend of the blade is approximately parabolic. As a result, in thevicinity of the conductor edge 5, the outer profile defined by theinsulation 2 is relatively wide compared to the thickness of theconductor edge 5. This aspect of the blade is shown in more detail inFIG. 2.

FIG. 2 is a magnified view of the area around the narrow gap region 7illustrated in FIG. 1. Shown are electrical conductive element 1, outerinsulation 2, conductor edge 5, and tissue 6. Sparks and other means ofelectrosurgical energy transfer occur mostly in the primary reactionregion 18, producing electrosurgical decomposition products which aredepicted by the dashed arrows 19. The electrosurgical decompositionproducts 19 include gases, such as steam, entrained particles, andliquids that have been heated. The volume of electrosurgicaldecomposition products 19, particularly the gases, will increase localgas pressure in the region 18 that force the electrosurgical productsout through the gap formed between the tissue 6 and the combination ofthe blade insulation 2 and conductor edge 5. For clarity, only oneconductor is shown in FIGS. 1 and 2, whereas in various embodimentsmultiple electrodes may be present.

The flow of the electrosurgical decomposition products 19 away from thefunctional area may be inhibited by the viscous drag that results fromthe narrowness and length of the gap as well as the tortuousity of thepath due to the roughness of the tissue, roughness of the blade, andcontact between the tissue 6 and the insulation 2 or conductor edge 5.The more the flow of electrosurgical decomposition products 19 isinhibited, the greater the local pressure rise and the longer thereaction products remain exposed to high temperatures in the region 18.In use, tissue 6 which contacts the insulation 2 in the primary reactionregion 18 may form temporary sealed pockets of gas, further inhibitingflow of reaction products. The inhibited flow from either viscous dragor temporarily sealed pockets is exacerbated when the blade is pressedinto the tissue 6 by the user as a natural part of the surgical incisionprocess. The result of these overall interactions is that theelectrosurgical decomposition products in the gap region 18 between thetissue 6 and the insulation 2 and conductor edge 5 becomes pressurizedto sufficient pressure to expel reaction products to achieve anapproximate and temporary equilibrium between the rate of materialforming and the rate of material leaving the region 18.

Even when the local pressure is high enough to force electrosurgicalproducts from the primary reaction region 18, the resulting localtemperature can be high enough to promote rapid pyrolysis and causeelectropyrolysis to occur. A major constituent of many tissues is water.The conversion of water to steam is a significant absorber of energywhen electrosurgical energy interacts with tissue. As a firstapproximation, the equilibrium temperature of saturated water and steamat the local pressure within the reactive region 18 can be used toestimate the minimum temperature that tissue in this region is exposedto during electrosurgery. For example, the estimated range of forcesapplied to blades by a user during an incision of tissue is about 0.15N/mm to about 0.625 N/mm, where N/mm is Newtons per millimeter of blademovement through the tissue. If a blade has a blunt (approximately flat)profile facing the tissue (as is the case with the broad parabolicprofile illustrated in FIG. 2) with a width of about 0.0508 mm (0.002inches), then the pressure applied to the tissue when the applied forceis 0.2 N/mm will be approximately 3.94 N/mm (3.94 MPA). At this pressurewater boils to steam at about 250° C. (482° F.), a temperature that ishigh enough for tissue to pyrolyze and leave carbon-rich residues.Carbon-rich residues are those in which at least some of theelectrosurgical decomposition products have a ratio of hydrogen atoms tocarbon atoms less than about 1. Such carbon-rich residues are believedto be a major constituent of eschar.

The wider the contact surface in the primary reaction region 18, thegreater the likelihood that tissue 6 will contact and momentarily stickto insulation 2 and the conductor edge 5, and thus, the greater thelikelihood that materials will be sealed briefly in fixed volumes (e.g.,pockets). As electrosurgical energy flows into a sealed volume withinthe reaction region 18, the equilibrium temperature will increase aspressure increases until the pressure reaches a point sufficiently highto burst through the seal of tissue stuck to the blade. Therefore, widecontact surfaces tend to lead to localized high pressure and hightemperature regions as well as increase the time that electrosurgicaldecomposition products reside within the vicinity of the primaryreaction region 18. Various embodiments use blade geometries thatprevent local temperatures proximate to the conductor edge 5 fromexceeding about 190° C. based upon saturated steam conditions andassuming an applied usage pressure of 0.2 N/mm. Some embodiments useblade geometries that limit the pressure on the edge of the blade toless than about 1.2 MPa.

Referring to FIG. 3, some embodiments use blade geometries which includean edge depth 20 of about 0.254 mm (0.010 inches) with a blade edge halfwidth 21 of less than about 0.5 mm (0.02 inches). In a furtherembodiment, the blade edge half width 21 is less than about 0.25 mm(˜0.01 inches), and in yet another embodiment the blade edge half width21 is less than about 0.12 mm (˜0.005 inches).

To achieve reaction conditions that lead to reduced smoke and eschar,blade profiles can be used that are generally tapered in the vicinity ofthe edge conductor such that a tangent to the insulation at theconductor edge forms an acute angle 8 (i.e., less than 90 degrees) withthe centerline of the blade as shown in FIGS. 6 and 8. Blade profileswith an acute insulation angle 8 are preferred over profiles that are ofan approximately parabolic form as shown in FIG. 1. FIG. 4 and FIG. 5illustrate geometries where the outer blade profile defined byinsulation 2 is shaped with more than a single smooth curve and thatjoin at the conductor edge 5.

FIG. 4 illustrates an embodiment where the conductive element 1 issurrounded by insulation 2 and the conductive element 1 has a concavetaper 3 that results in a narrow conductor edge 5. In the embodimentillustrated in FIG. 4, the insulation 2 covering the conductive element1 reduces in thickness toward the narrow edge until the conductiveelement metal is exposed forming the conductor edge 5. In thisembodiment, the insulation 2 has an insulation taper 4 that also has agenerally concave shape defined by the curves that smoothly terminate atthe conductor edge 5. This geometry presents few opportunities fortissue to press against the edge of the blade to form seals or tortuouspaths compared with the blade profile shown in FIG. 1.

FIG. 5 illustrates an embodiment similar to that shown in FIG. 4 exceptthat the conductive element taper 3 and insulation taper 4 areapproximately linear (i.e., flat) instead of being concave. As with theembodiment shown in FIG. 4, the geometry of the embodiment shown in FIG.5 provides little opportunity for tissue to press against the edge ofthe blade and form seals or tortuous paths compared to the bladegeometry shown in FIG. 1. Other embodiments include an insulation taperformed such that the surface of the insulation follows more than onecurve defining the insulation taper in the vicinity of the conductoredge 5.

FIG. 6 illustrates a blade embodiment that includes an acute insulationangle 8. The insulation angle is the angle formed between a line tangentto the insulation bevel 4 at the conductor edge 5 and a line parallel tothe centerline of the blade edge 5. FIG. 7 illustrates the insulationangle 8 that occurs when the insulation taper 4 is be characterized by asingle continuous smooth curve (a broad parabola in this case) comparedto FIG. 6 where the insulation angle 8 that occurs is characterized bytwo curves (flat lines in this case) that essentially intersect at theconductor edge 5. FIG. 8 illustrates the case where the insulation 2transitions from one curve to another before two separate curvesintersect near the conductor tip 5 forming an acute insulation angle 8.

In the various embodiments, the insulation angle 8 should be less than90 degrees, and preferably should be less than about 60 degrees, morepreferably less than about 50 degrees, and still more preferably lessthan about 45 degrees.

A number of geometries for the taper portion can be employed to achievean insulation angle of less than 90 degrees. FIG. 3 illustrates a narrowparabola geometry with an acute insulation angle. FIG. 4 illustrates aconcave geometry which results in an acute insulation angle. FIGS. 5 and6 illustrate a flat (i.e., linear) taper with an acute insulation angle.FIG. 8 illustrates a two-curve geometry resulting in an acute insulationangle. FIG. 9 illustrates a blade cross-section that has an insulationtaper 4 that is concave. FIG. 9 also illustrates a conductive element 1with a concave tapered region 3 that reduces down to form the conductoredge 5. Embodiments with conductive elements that have substantiallyconcave tapers down to the edge facilitate the production of an outerinsulation profile that is also concave as FIG. 9 illustrates.

The blade thickness profile embodiments illustrated in FIGS. 1-9 can beused for a cutting blade with a planar shape similar to a scalpel, inwhich case the width of the blade would extend out of the page.Additionally, thickness profile embodiments illustrated in FIGS. 1-9 canbe used with a needle electrode, in which case the width extending outof the page would be approximately equal to the thickness profile, anexample of which is illustrated in FIG. 14.

Restricting the amount of time that tissue and electrosurgicaldecomposition products are exposed to electrosurgical energy reduces theamount of eschar and smoke produced and reduces the amount of tissuedamage. When the edge of blade contacts tissue for a period of timelonger than is necessary to achieve the predetermined surgical effect,such as cutting, then more smoke and eschar are produced and more tissuedamage occurs. The various embodiments include insulation 2 over theconductive element 1 which insulates the outside of the blade except forthe exposed conductor edge 5, as has been illustrated in FIGS. 1-9. Theinsulation 2 restricts the flow of electrosurgical energy from theconductive element 1 to the tissue 6 except at the conductor edge 5. Toserve this function, the insulation 2 needs to be of an adequatedimension so as to restrict or prevent the flow electrosurgical energy.However, too much insulation may make the blade width excessive.

The conductive element 1 both conveys electrical energy to the conductoredge 5 and conducts thermal energy away from the conductor edge 5 tohelp keep the blade relatively cool. Making the conductor edge 5 thickwould facilitate conducting heat away from the edge, but if the edge istoo thick then more sealing of tissue against the edge can occur withthe coincident increase in smoke and eschar production and tissuedamage. The ability of the conductive element 1 to remove thermal energyfrom the conductor edge 5 depends on the thermal conductivity of thematerial from which it is made. This relationship between thermalconductivity and the width of the edge can be expressed as the productof thermal conductivity and the width of the conductor edge 5, such thata poorer thermal conductor needs a wider path than a better thermalconductor. As used herein, the term “thermal path conductance” refers tothe product of the conductive element material's thermal conductivityand the width of the thermal flow path, where the thermal conductivityis measured in W/m/° K at about 300° K and the width is measured inmeters, leading to the units of thermal path conductance being W/° K.The various embodiments can have a thermal path conductance at theconductor edge of at least 0.0002 W/° K, preferably of at least 0.0003W/° K, more preferably of at least 0.0006 W/° K, and still morepreferably of at least 0.001 W/° K. For example, if the thermal pathwidth is 0.0005 inches (1.27E-5 m) and the material used is molybdenumhaving a thermal conductivity of about 138 W/m/° K, then the thermalpath conductance is about 0.00175 W/° K. In a blade having a planarconfiguration like a scalpel, the width of the thermal path will be thethickness of the blade at the edge.

To reduce the amount of tissue heated, the electrosurgical energy isfocused in the various embodiments. One method of focusing the energy isto insulate the blade except for an exposed edge. Preferably, theexposed conductor edge 5 of the conductive element 1 is flush with theinsulation layer 2 so as to avoid any recessed pockets and anunnecessarily broad reaction area such as formed if the electrode isrecessed into a pocket in the insulation, the edge is coated with aninsulator, or the edge is rounded. In some embodiments, the conductoredge 5 adjoins the insulating layer 2 to form a singular taperedexterior surface. Focusing electrosurgical energy is further facilitatedby having a narrow conductor edge 5.

A flush, non-recessed conductor edge 5 further facilitates theelectrosurgical process beyond the focus of electrosurgical energy. Ifthe conductor edge is recessed within the insulation, then a pocketexists where tissue or electrosurgical decomposition products canaccumulate and remain exposed for long durations to electrosurgicalenergy, thus promoting continued pyrolysis and electropyrolysis. In anembodiment, no pockets or recesses should exist where tissue orelectrosurgical decomposition products can accumulate. Therefore, gapsor recesses between the conductor edge and the insulation are avoided invarious embodiments. By adjoining the conductor edge with the insulatinglayer to form a flush exterior tapered surface with no gaps or recesses,the singular exterior tapered surface can take on a strictly convexshape immediately adjacent to the conductor edge. This embodimentreduces or eliminates opportunities for trapping tissue during use. Awayfrom the conductor edge the profile of the insulation taper can beconcave. This embodiment reduces residency time at high temperatures andreduces pressure which reduces the equilibrium steam temperature.

In addition to avoiding gaps or recess between the conductor edge 5 andthe insulation layer 2, the conductor edge 5 itself should not haverecesses in the conductive element material that might promote thetrapping of tissue or electrosurgical decomposition products. Preferablythe conductor edge 5 is relatively smooth and does not have recessesalong its length or width, such sawtooth, gaps, pockets or holes thatare larger than about 32 microinches.

Embodiments of the invention include conductor edge shapes that arepointed, terminate to an acute angle, or are flat. Preferably, the shapeof the conductor edge 5 is not rounded. Preferably the conductor edgehas a thickness less than about 0.005 inches, more preferably less thanabout 0.002 inches, more preferably less than about 0.001 inches, andeven more preferably about 0.0005 inches or less.

The thickness of the insulation layer, particularly at the areaproximate to the conductor edge, affects the overall thickness of theedge of the blade. Enough insulation needs to be present to restrict therate of energy transfer out the sides of the blade into tissue orelectrosurgical decomposition products to prevent or reduce continuedchanges in those materials. Restricting the rate of energy transfer outthe sides is particularly important near the conductor edge wheretemperatures will be highest. If the insulation is thicker thannecessary to prevent continued changes in tissue or electrosurgicaldecomposition products, then the blade will be wider than necessary nearthe conductor edge, which increases the opportunities for sealing tissueagainst the conductor edge or the insulation near the conductor edge.

When conductive element 1 is tapered so that it is thinnest at theconductor edge 5, as illustrated in FIGS. 1-9, the temperature of theconductive element will decrease as the distance from the conductor edge5 increases. Therefore, the thickest insulation needs to be near theconductor edge 5, allowing the shape of the insulation 2 to have atapered region 4 that needs to be no thicker than it is near theconductor edge 5. The thickness of the insulation at the conductor edgecan be at least one half of the thickness of the conductor edge and morepreferably at least equal to about the thickness of the conductor edge.For example, if the conductor edge can have a thickness of 0.001 inchesthen the insulation surrounding the conductor edge preferably has athickness of about 0.0005 inches and preferably has a thickness of about0.001 inches.

The main portion of the conductive element 1 should be thick enough toreadily conduct heat away from the conductor edge 5. The width of theconductive element 1 can have a thickness before the taper portion 3that is at least about 5 times as thick as the conductor edge 5,preferably at least about 10 times as thick as the conductor edge 5, andmore preferably at least about 20 times as thick as the conductor edge5. For example, if the conductor edge is 0.001 inches thick and theconductive element thickness before the taper begins is 0.020 inches,then the ratio of the thickness of the conductive element to thethickness of the conductor edge is 20.

In addition to the edge geometry, the overall configuration of the bladecontributes the generation of excessive decomposition products andincreased tissue damage. For example, FIG. 10 illustrates a bladeconnected to shaft 11 that has blade body 10 with intersecting conductoredges 13 that subtend intersecting edge angle 14. In use, the bladeproduces the predetermined surgical effect (e.g., cutting) when theblade is moved through tissue in the direction indicated by arrow 12.This blade configuration moving through tissue 6 is illustrated in FIG.11. As the blade 10 moves through tissue, an electrosurgically affectedtissue region 16 is created. As the blade 10 moves through tissue 6, theleading corner 13 b initially contacts the tissue near the bottom of theblade and bottom edge 13 a then continues to supply electrosurgicalenergy to the already affected tissue as the blade is moved. Thus, thebottom conductor edge 13 a prolongs the residence time that the tissuealong bottom conductor edge 13 a is affected by electrosurgical energy.The prolonged residence time increases smoke and eschar production andincreases tissue damage. The intersecting edge angle 14 influenceswhether such prolonged residence time occurs and the closer that theangle is to 180 degrees (i.e., the less there is a trailing edge) theless likely that prolonged residence time occurs. If the intersectingedge angle 14 is made more acute, the situation depicted in FIG. 12occurs. While the residence time of tissue near the trailing edge 15 isreduced in the configuration illustrated in FIG. 12, the trailingconductor edge 15 following the incision does continue supplyingelectrosurgical energy to tissue 16 that has already been affected byelectrosurgical energy delivered from the leading edge 13.

The intersecting conductor edges 13 in FIGS. 10-12 provide a point ofconcentration for electrosurgical energy when the blade first contactstissue 6 facilitating starting an electrosurgical effect such ascutting. Thus, such a concentration is desirable because it makesstarting or controlling the electrosurgical effect easier. In variousembodiments, the intersecting conductor edges angle does not allow theblade to be oriented during use such that tissue is exposed to an activeedge (and thus exposed to electrosurgical energy) for a prolongedresidence time. In some embodiments, the intersecting edge angle isobtuse, in some embodiments the intersecting edge angle is greater thanabout 160 degrees, and in an embodiment the intersecting edge angle isapproximately equal to about 180 degrees. The example embodimentgeometries illustrated in the figures show edges that are substantiallystraight. Other embodiments include edges that have one or more curves,such as edges comprised of one or more parts of ellipses, circles,parabolas, or hyperbolas, and edges composed of a multiplicity ofstraight sections as well as edges composed of one or more combinationsof straight sections and curves.

In an embodiment, only one conductor edge is present as illustrated inFIG. 13. The single conductor edge 13 is also the leading edge 13 c thatfirst transfers electrosurgical energy to tissue 6 producing theelectrosurgically affected tissue region 16. The trailing edge 13 d isnot a functional surface, i.e., it does not transfer electrosurgicalenergy to tissue because it does not have an exposed surface (conductoredge) capable of transferring electrosurgical energy to tissue. Theblade illustrated in FIG. 13 comes to a region 13 e whereelectrosurgical energy is concentrated when the blade first contactstissue 6.

In an embodiment the width of the blade is made sufficiently short sothat the blade comes to a point without an edge, such as illustrated inFIG. 14. In this embodiment, the point 17 may have a substantially(though not necessarily) circular cross-section as it tapers from thebody 10 to the tip 17. This embodiment is referred to herein as a needleelectrode since its width is approximately equal to its thickness;however, its cross section may be oblong, oval, square or other shape inaddition to, or instead of, circular and may be comprised of one or morecurves or portions of curves such as ellipses, parabolas, or hyperbolas,possibly in conjunction with one or more substantially straight sectionsor may be comprised of a multiplicity of straight segments forming apolygon, not necessarily a regular polygon. This profile need notnecessarily be strictly convex. Also, the profile may have one or moreopenings or crevices passing at least partially along the length of theneedle.

In various embodiments, the blade has one or more conductor edgesconfigured so that they cause electrosurgical energy to enter tissueonly at the time when the blade first encounters tissue that has not yetexperienced the predetermined electrosurgical effect. In someembodiments, the blade has one or more conductor edges configured sothat they have a region that concentrates electrosurgical energy whenthe blade first contacts tissue, such as in a region that approximates apoint, and such blade has one or more conductor edges configured so thatthey cause electrosurgical energy to enter tissue only at the time whenthe blade first encounters tissue that has not yet had the predeterminedelectrosurgical affect occur. For embodiments where the blade is to beused as a scalpel for cutting and other electrosurgical functions, theembodiments may have a single conductor edge that comes to a pointapproximately.

By employing various embodiments, a higher crest factor electrosurgicalenergy can be used for the predetermined surgical effect of cuttingwithout excessive damage to tissue or generation of smoke or eschar.Crest factor is the ratio of peak voltage to the RMS voltage. Duringcutting, crest factors of less than about 5 and typically less thanabout 3 are used. For a predetermined surgical effect of moderatecoagulation crest factors of about 4 to 5 are typically used. To achievethe predetermined surgical effect of aggressive coagulation, crestfactors greater than 8, typically of about 9, are used. If cuttingtissue is attempted with conventional blades and crest factors that aretoo high, the cutting effect will be very poor and blades that do notincorporate features of the various embodiments will immediatelyaccumulate large masses of adherent tissue that prevents further useuntil the blade is cleaned. Moreover, at a crest factor of about 8ordinary electrosurgical blades do not cut at all or very poorly. Thus,the drawbacks of conventional electrosurgical blades prevent the use ofhigh crest factors for cutting. By focusing electrosurgical energy andreducing the residence time during which tissue is exposed toelectrosurgical energy the various embodiments of the present inventionallow use of higher crest factors for cutting.

Using high crest factors for cutting enhances hemostasis. Enhancinghemostasis is particularly beneficial when the tissue being affected ishighly vascularized, such as the liver. One embodiment provides a bladethat cuts with enhanced hemostasis that comprises an insulatedconductive element that tapers to one or more conductor edges that areat least partially exposed such that they can transfer electrosurgicalenergy to tissue and that have thermal path conductance that is at least0.0002 W/° K, wherein the exposed edge is no thicker than about 0.005inches and the blade is connected to an ESU configured to supplyelectrosurgical power with a crest factor of about 5 or larger. Anembodiment provides a blade that cuts with the ESU configured to supplyelectrosurgical power with a crest factor of about 8 or larger.

In an embodiment, a method of using an electrosurgical instrumentincludes connecting an electrosurgical instrument having a bladeconfigured according to various embodiments to an ESU, adjusting the ESUto output RF power with a wave form (i.e., shape of the RF power versustime) having a crest factor of about 5 or higher, and bringing theelectrosurgical instrument close to or in contact with tissue to make anincision or conduct a cutting procedure (i.e., the predeterminedelectrosurgical effect includes cutting tissue). In another embodiment,a method of using an electrosurgical instrument includes connecting anelectrosurgical instrument having a blade configured according tovarious embodiments to an ESU, adjusting the ESU to output RF power witha wave form having a crest factor of about 8 or higher, and bringing theelectrosurgical instrument close to or in contact with tissue to make anincision or conduct a cutting procedure.

In various embodiments, the outer insulating layer may have a maximumthermal conductance of about 1.2 W/cm²° K when measured at about 300° K,preferably about 0.12 W/cm²° K or less when measured at about 300° K,and more preferably about 0.03 W/cm² ° K when measured at about 300° K.As used herein, thermal conductance refers to a measure of the overallthermal transfer across any given cross section (e.g. of the insulationlayer), taking into account both the thermal conductivity of thematerials comprising such layer and the thickness of the layer (i.e.thermal conductance of layer=thermal conductivity of material comprisingthe layer (W/cm ° K)/thickness of the layer (cm)).

In relation to the various embodiments, the insulation layer should alsoexhibit a dielectric withstand voltage of at least the peak-to-peakvoltages that may be experienced by the electrosurgical instrumentduring surgical procedures. The peak voltages will depend upon thesettings of the RF source employed, as may be selected by clinicians forparticular surgical procedures. In various embodiments, the insulationlayer should exhibit a dielectric withstand voltage of at least about 50volts, and more preferably, at least about 150 volts. As used herein,the term “dielectric withstand voltage” means the capability to avoid anelectrical breakdown (e.g. an electrical discharge through theinsulating layer) for electrical potentials up to the specified voltage.

In some embodiments, the insulating or electrode bonding layer maycomprise a porous ceramic material that has had at least the pores onthe surface sealed to prevent or impede the penetration of biologicalmaterials into the pores. Such ceramic may be applied to the electrodesvia dipping, spraying, etc, followed by curing via drying, firing, etc.Preferably, the ceramic insulating layer should be able to withstandtemperatures of at least about 2000° F.

The ceramic insulating layer may comprise various metal/non-metalcombinations, including for example compositions that comprise thefollowing: aluminum oxides (e.g. alumina and Al₂O₃), zirconium oxides(e.g. Zr₂O₃), zirconium nitrides (e.g. ZrN), zirconium carbides (e.g.ZrC), boron carbides (e.g. B₄C), silicon oxides (e.g. SiO₂), mica,magnesium-zirconium oxides (e.g. (Mg—Zr)O₃), zirconium-silicon oxides(e.g. (Zr—Si)O₂), titanium oxides (e.g., TiO₂) tantalum oxides (e.g.Ta₂O₅), tantalum nitrides (e.g. TaN), tantalum carbides (e.g., TaC),silicon nitrides (e.g. Si₃N₄), silicon carbides (e.g. SiC), tungstencarbides (e.g. WC) titanium nitrides (e.g. TiN), titanium carbides(e.g., TiC), niobium nitrides (e.g. NbN), niobium carbides (e.g. NbC),vanadium nitrides (e.g. VN), vanadium carbides (e.g. VC), andhydroxyapatite (e.g. substances containing compounds such as3Ca₃(PO₄)₂Ca(OH)₂Ca₁₀(PO₄)₆(OH)₂Ca₅(OH)(PO₄)₃, and Ca₁₀H₂O₂₆P₆). One ormore ceramic layers may be employed, wherein one or more layers may beporous, such as holes filled with one or more gases or vapors. Suchporous compositions will usually have lower thermal conductivity thannonporous materials. An example of such materials is foam, such as anopen cell silicon carbide foam. Such porous materials have thedisadvantage that they allow fluids, vapors, or solids to enter thepores whereby they are exposed to prolonged contact with hightemperatures which can lead to thermal decomposition or oxidation andproduce smoke or other noxious or possibly dangerous materials. Sealingthe surface of the ceramic prevents such incursions, while substantiallypreserving the beneficial reduced thermal conductivity of the pores.

Ceramic coatings or electrode bonding materials may also be formed inwhole or part from preceramic polymers that when heated form materialscontaining Si—O bonds able to resist decomposition when exposed totemperatures in excess of 1200° F., including compositions that use oneor more of the following as preceramic polymers: silazanes,polysilzanes, polyalkoxysilanes, polyureasilazane, diorganosilanes,polydiorganosilanes, silanes, polysilanes, silanols, siloxanes,polysiloxanes, silsesquioxanes, polymethylsilsesquioxane,polyphenyl-propylsilsesquioxane, polyphenylsilsesquioxane,polyphenyl-vinylsilsesquioxane. Preceramic polymers may be used to formthe ceramic coating by themselves or with the addition of inorganicfillers such as clays or fibers, including those that contain siliconoxide, aluminum oxides, magnesium oxides, titanium oxides, chromeoxides, calcium oxides, or zirconium oxides.

Ceramic coatings may also be formed by mixing one or more colloidalsilicate solutions with one or more filler materials such as one or morefibers or clays. The filler materials can contain one or more materialsthat have at least 30 percent by weight Al₂O₃ or SiO₂ either alone orcombined with other elements, such occurs in kaolin or talc. Thecolloidal silicate and filler mixture may optionally contain othersubstances to improve adhesion to electrode surfaces or promoteproducing a sealed or hydrophobic surface. Representative examples ofcolloidal silicate solutions are alkali metal silicates, including thoseof lithium polysilicate, sodium silicate, and potassium silicate, andcolloidal silica. Fibers may include those that contain in part orwholly alumina or silica or calcium silicate, and Wollastonite. Claysmay include those substances that are members of the smectite group ofphyllosilicate minerals. Representative examples of clay mineralsinclude bentonite, talc, kaolin (kaolinite), mica, clay, sericite,hectorite, montmorillonite and smectite. Various embodiments use atleast one of kaolin, talc, and montmorillonite. These clay minerals canbe used singly or in combination. In various embodiments, at least onedimension, such as diameter or particle size, of at least one of thefiller materials has a mean value of less than 200 micrometers and morepreferably has a mean value of less than 50 micrometers and even morepreferably has a mean value of less than 10 microns and still morepreferably has a mean value less than 5 microns Substances that may beadded to promote adhesion or production of a sealed or hydrophobicsurface include those that increase the pH of the mixture, includingsodium hydroxide or potassium hydroxide, and hydrolysable silanes thatcondense to form one or more cross-linked silicone-oxygen-siliconstructures.

Sealing a porous insulator is accomplished not by coating the ceramic inthe sense that electrosurgical accessories have been coated with PTFE,silicone polymers and other such materials. Best surgical performanceoccurs when accessories are thin, therefore pores are best filled by amaterial that penetrates the surface of the porous material and sealsthe pores. Some residual material may remain on the surface, but suchmaterial is incidental to the sealing process.

Sealing materials need to withstand temperatures exceeding 400° F. andmore preferably withstand temperatures exceeding 600° F. Silicates andsolutions containing or forming silicates upon curing can be used. Othermaterials may be used, including silicone and fluorosilicones. Forsealing, the materials need to have low viscosity and other propertiesthat enable penetration into the surface of the porous insulator.Traditional silicone and fluorosilicone polymer-forming compounds do nothave these properties unless they are extensively diluted with athinning agent, such as xylene or acetone.

A sealed porous insulation may be employed to yield an average maximumthermal conductivity of about 0.006 W/cm-° K or less where measured at300° K. The insulating layer outside of the blade can have a thicknessof between about 0.001 and 0.2 inches, and preferably between about0.005 and 0.100 inches and more preferably between about 0.005 and 0.050inches.

A coating that is applied as a single substance that upon curing doesnot require sealing may also be used for the outer insulation or as thebonding material between electrodes. Examples of such coatings includethose formed from mixtures that use one or more of the aforementionedcolloidal silicates and clays and also use one or more substances thatreduce the surface free energy of the surface. Substances that reducethe surface free energy include: halogenated compounds, fluoropolymercompounds, such as PTFE and PFA, including aqueous dispersions of suchcompounds; and organofunctional hydrolysable silanes, including thosecontaining one or more fluorine atoms on one or more pendant carbonchains.

In some embodiments, a hydrolysable silane is a component in the coatingor in the insulating material between electrodes, with the hydrolysablesilane having one or more halogen atoms and having a general formula ofCF₃(CF₂)_(m)(CH2)_(n)Si(OCH₂CH₃)₃ where m is preferably less about 20and more preferably about 5 or less and where n is preferably about 2.Other groups besides (OCH₂CH₃)₃, such as those based on ethyl groups,may be used and fall within the scope of the various embodiments whenthey also are hydrolysable. Other halogens, such as chlorine, may besubstituted for the fluorine, although these will typically produceinferior results.

Preferably, the surface energy (also referred to as the surface tensionor the surface free energy) of the coating is less than about 32millinewtons/meter and more preferably less than about 25millinewtons/meter and even more preferably less than about 15millinewtons/meter and yet more preferably less than about 10millinewtons/meter.

In an embodiment, the conductive elements or conductor edges or both ofthe electrosurgical instrument may be configured to have a thermalconductivity of at least about 0.35 W/cm ° K when measured at about 300°K. By way of example, the conductive elements or conductor edges or bothmay comprise at least one metal selected from the group including:silver, copper, aluminum, gold, tungsten, tantalum, columbium (i.e.,niobium), and molybdenum. Alloys comprising at least about 50% (byweight) of such metals may be employed, and even more preferably atleast about 90% (by weight). Additional metals that may be employed insuch alloys include zinc.

In various embodiments, at least a portion of the conductor edge is notinsulated (i.e. not covered by the outer insulating layer). Inconnection therewith, when the conductor edge comprises copper, theexposed portion may be coated or plated (e.g. about 10 microns or less)with a biocompatible metal. By way of example, such biocompatible metalmay be selected from the group including: nickel, silver, gold, chrome,titanium tungsten, tantalum, columbium (i.e., niobium), and molybdenum.

In some embodiments, the conductive element, conductor edge, or both maycomprise two or more layers of different materials. More particularly,at least a first metal layer may be provided to define at least part ofthe conductor edge that is functional to convey electrosurgical energyto tissue as described above. Such first metal layer may comprise ametal having a melting temperature greater than about 2600° F.,preferably greater than about 3000° F., and more preferably greater thanabout 4000° F., thereby enhancing the maintenance of a desiredperipheral edge thickness during use (e.g. the outer extreme edge notedabove). Further, the first metal layer may have a thermal conductivityof at least about 0.35 W/cm ° K when measured at 300° K.

For living human/animal applications, the first metal layer may comprisea first material selected from a group including: tungsten, tantalum,columbium (i.e., niobium), and molybdenum. All of these metals havethermal conductivities within the range of about 0.5 to 1.65 W/cm ° Kwhen measured at 300° K. Alloys comprising at least about 50% by weightof at least one of the group of materials may be employed, and morepreferably at least about 90% by weight.

In addition to the first metal layer, the conductive element may furthercomprise at least one second metal layer on the top and/or bottom of thefirst metal layer. A first metal layer as noted above can be provided ina laminate arrangement between top and bottom second metal layers. Toprovide for rapid heat removal, the second metal layer(s) preferably hasa thermal conductivity of at least about 2 W/cm ° K. By way of example,the second layer(s) may advantageously comprise a second materialselected from the group including: copper, gold, silver and aluminum.Alloys comprising at least about 50% of such materials may be employed,and more preferably at least about 90% by weight. It is also preferablethat the thickness of the first metal layer and of each second metallayer (e.g. for each of a top and bottom layer) be between about 0.001and 0.25 inches, and even more preferably between about 0.005 and 0.1inches.

One or more of the conductor edges may be plated with gold or silver oralloys thereof to confer added oxidation resistance to the portions ofthe electrodes exposed to tissue or current flow or both. Such platingmay be applied using electroplating, roll-bonding or other means eitherafter assembly or prior to assembly of the electrodes to form blades.The plating thickness can be at least about 0.5 micrometers andpreferably at least about 1 micrometer.

As may be appreciated, multi-layered metal bodies of the type describedabove may be formed using a variety of methods. By way of example,sheets of the first and second materials may be roll-bonded togetherthen cut to size. Further, processes that employ heat or combinations ofheat and pressure may also be utilized to yield a laminated electrode.

In some embodiments, the electrosurgical instrument may further comprisea heat sink for removing thermal energy from the conductor edge,conductive element, or both. In this regard, the provision of a heatsink helps establishes a thermal gradient for conducting heat away fromthe conductor edge, thereby reducing undesired thermal transfer to atissue site. More particularly, it is preferable for the heat sink tooperate so as to maintain the maximum temperature on the outside surfaceof the insulating layer at about 160° C. or less, more preferably atabout 80° C. or less, and most preferably at 60° C. or less. Relatedly,it is preferable for the heat sink to operate to maintain an averageconductive element temperature of about 500° C. or less, more preferablyof about 200° C. or less, and most preferable of about 100° C. or less.

In an embodiment, the heat sink may comprise a vessel including a phasechange material that either directly contacts a portion of theelectrodes (e.g. a support shaft portion) or that contacts a metalinterface provided on the vessel which is in turn in direct contact witha portion of the electrodes (e.g. a support shaft portion). Such phasechange material changes from a first phase to a second phase uponabsorption of thermal energy from the electrodes. In this regard, thephase change temperature for the material selected should preferably begreater than the room temperature at the operating environment andsufficiently great as to not change other than as a consequence ofthermal heating of the electrosurgical instrument during use. Such phasechange temperature should preferably be greater than about 30° C. andmost preferably at least about 40° C. Further, the phase changetemperature should be less than about 225° C. Most preferably, the phasechange temperature should be less than about 85° C.

The phase change may be either from solid to liquid (i.e., the phasechange is melting) or from liquid to vapor (i.e., the phase change isvaporization) or from solid to vapor (i.e., the phase change issublimation). More practical phase changes to employ are melting andvaporization. By way of example, such a phase change material maycomprise a material that is an organic substance (e.g., fatty acids,such as stearic acid, hydrocarbons such as paraffins) or an inorganicsubstance (e.g., water and water compounds containing sodium, such as,sodium silicate (2-)-5-water, sodium sulfate-10-water).

In an embodiment, the heat sink may comprise a gas flow stream thatpasses in direct contact with at least a portion of the electrodes. Suchportion may be a peripheral edge portion and/or a shaft portion of theelectrodes that is designed for supportive interface with a holder forhand-held use. Alternatively, such portion may be interior to at least aportion of the electrodes, such as interior to the exposed peripheraledge portion and/or the shaft portion of the electrodes that is designedfor supportive interface with a holder for hand-held use. In yet otherembodiments, the heat sink may simply comprise a thermal mass (e.g.disposed in a holder).

In an embodiment, an electrosurgical instrument comprises a main bodyportion having a blade-like configuration at a first end and anintegral, approximately cylindrical shaft at a second end. The main bodymay comprise a highly-conductive metal and/or multiple metal layers asnoted. At least a portion of the flattened blade end of the main bodycan be coated with a ceramic-based and/or silicon-based, polymerinsulating layer, except for the peripheral edge portion thereof. Thecylindrical shaft of the main body can be designed to fit within anouter holder that can be adapted for hand-held use by medical personnel.Such holder may also include a chamber comprising a phase-changematerial or other heat sink as noted hereinabove. Additionally, one ormore control elements, such as buttons or switches, may be incorporatedinto the holder for selectively controlling power or other aspects ofthe device's operation, such as the application of one or more,predetermined, electrosurgical signal(s) from an RF energy source to theblade via the shaft of the main body portion.

In some embodiments, the conductive element 1 with its surroundinginsulation 2 are provided as a single use sterile disposable blade thatcan be coupled to a holder or handle which may be reusable or a singleuse device. In such embodiments, the conductive element 1 includeselectrical connector surfaces on the end proximal end (i.e., the end ofthe electrodes closest to the handle in use) suitable for electricallyconnecting to compatible electrical connector surfaces, such as a sleevewithin the holder. The connector surfaces may also serve as a mechanicalcoupling so that by inserting the blade into the holder connector, theblade is rigidly held by the holder. In such embodiments, the reusableholder or handle may include one or more control components, such asbuttons or switches, for selectively controlling power or other aspectsof the device's operation, such as controlling the application of one ormore, predetermined, electrosurgical signal(s) from an RF energy sourceto the blade via the shaft of the main body portion. In such anembodiment, a single use sterile disposable blade can be sealed in asterile package, which may a single use dipsolable handle and/or includeinstructions for assembly and use, to provide an electrosurgical kit tobe opened at the time surgery is to be performed.

In some embodiments, the conductive element 1 with its surroundinginsulation 2 is fixedly coupled to a holder or handle 21 as a single useelectrosurgical assembly 20, such as illustrated in FIG. 15. In suchembodiments, the electrosurgical assembly 20 includes a blade 10mechanically and electrically coupled to the holder or handle 21, suchas by a connector 22. An electrical connector 23 on the holder or handle21 can be provided to connect, such as by means of a cable 29, to an ESUor similar source of radio frequency (RF) AC power. An internalconductor 24 conducts the RF power from the connector 23 at one end ofthe handle 21 to the blade 10 at the other end of the handle 21.Electrical and thermal insulation 25 can be provided to isolate powerbeing conducted in the internal conductor 24 from the holder exterior26, thereby protecting the clinician using the electrosurgical assembly20. The blade connector 22 may also include electrical insulation toelectrically isolate the blade 10 from the handle exterior 26. Controlelements 27, 28 may be provided on the handle 21 to enable a user toactivate, deactivate and otherwise control power provided by the ESU orRF power source. The handle 21 may be shaped to enable a user tocomfortably hold or otherwise manipulate the assembly 20, provided witha surface material or surface texture, such as roughening, to enhance auser's grip and other ergonomic features to aid a clinician inmanipulating the disposable electrosurgical assembly 20. The handle 21may be reusable or a single use disposable device. A cable 29connectable to the connector 23 and fitted with a suitable electricalplug 30 can be used to electrically couple the handle 21 to the ESU. Thecable 29 may be reusable or disposable. In an embodiment, the cable 29and plug 30 are included as part of the electrosurgical assembly 20. Inan embodiment including one or more control elements 27, 28 on theholder or handle 21, electronic connectors may be provided within cable29 for relaying control signals to the ESU.

In some embodiments, the a single use sterile electrosurgical assembly20 can be sealed in a sterile package, which may include a cable 29and/or instructions for assembly and use, to provide an electrosurgicalkit to be opened at the time surgery is to be performed.

Conventional electrosurgical signals may be advantageously employed incombination with one or more of the above-noted electrosurgicalinstrument embodiments. In particular, the inventive electrosurgicalinstrument yields benefits when employed with electrosurgical signalsand associated apparatus of the type described in U.S. Pat. No.6,074,387, hereby incorporated by reference in its entirety.

The apparatus and methods for reducing smoke, eschar, and tissue damageaccording to various embodiments may be applied in conjunction withother methods for reducing the local heating that promotes the excessiveelectrosurgical tissue decomposition which leads to smoke, eschar, andtissue damage. Such additional methods for reducing local heatinginclude providing for an effective level of heat removal away fromfunctional portions of an electrosurgical instrument and/or by otherwiseenhancing the localized delivery of an electrosurgical signal to atissue site, such as by reducing the exposed areas of either or bothfunctional and nonfunctional areas by using thermal insulation.

While the present invention has been disclosed with reference to certainpreferred embodiments, numerous modifications, alterations, and changesto the described embodiments are possible without departing from thesphere and scope of the present invention, as defined in the appendedclaims. Accordingly, it is intended that the present invention not belimited to the described embodiments, but that it have the full scopedefined by the language of the following claims, and equivalentsthereof.

1. A method for performing electrosurgery to achieve a predeterminedelectrosurgical effect on tissue, comprising: applying radiofrequencypower having a crest factor of about 5 or greater to an electrosurgicalinstrument comprising an electrically conductive element having a firstsection and a first tapered section terminating at a conductor edge,wherein the first tapered section includes a beveled surface having aconcave shape, and an insulation layer having a second tapered sectionoverlaying the conductive element which tapers on a side of the firsttapered section to expose the conductor edge forming a primary reactionregion, wherein the second tapered section has a concave shape; andpositioning the electrosurgical instrument near tissue.
 2. The methodfor performing electrosurgery according to claim 1, wherein the appliedradiofrequency power has a crest factor of about 8 or higher.
 3. Amethod of for performing electrosurgery to achieve a predeterminedelectrosurgical effect on tissue, comprising: connecting a source ofradio frequency power to an electrosurgical instrument comprising anelectrically conductive element having a first section and a firsttapered section terminating at a conductor edge, wherein the firsttapered section includes a beveled surface having a concave shape, andan insulation layer having a second tapered section overlaying theconductive element which tapers on a side of the first tapered sectionto expose the conductor edge forming a primary reaction region, whereinthe second tapered section has a concave shape; adjusting the source ofradio frequency power to output a wave form having a crest factor equalto or greater than about 5; positioning the electrosurgical instrumentnear tissue; and performing an incision in the tissue using theelectrosurgical instrument.
 4. The method for performing electrosurgeryaccording to claim 3, wherein the source of radio frequency power isadjusted to output a wave form having a crest factor equal to or greaterthan about 8.